1. Field of the Invention
The invention relates generally to magnetic head assemblies, and more particularly to narrow magnetic transducing cores for use in a head shoe of the type used in magnetic recording systems and improved means for manufacturing such cores.
The invention is based on the realization that as regards read/write heads used in computer peripherals such as data acquisition, data storage, data retrieval and others to record statistical or other information on magnetic tapes, disks or drums, the heads may be provided with a plurality of closely spaced, parallel channels or cores each including a core gap, and the narrower the cores, the higher the track density per inch on the recording medium.
2. Description of the Prior Art
In magnetic storage systems, a transducer head is mounted over a moving recording medium, such as a magnetic drum, disk or tape, at a small distance from the surface of the medium. The head carries a plurality of magnetic read/write cores, generally parallel to the surface of the medium, each sensing the magnetic condition of one or a plurality of discrete data tracks on the medium as the surface passes beneath the head. With the need for high density and high frequency recording, the dimensions of the transducing cores and gaps have been made progressively smaller. Due to inadequate manufacturing methods in the past associated with such multicore heads, high yield production of the head assembly has been difficult to obtain because of the need for fine positioning of the delicate cores in the head shoe and because of the criticalness of the gap dimensions.
One known technique for producing narrow head cores is to initially bond a pair of discrete core bars together and form the same into a "sandwich" which, subsequently, is sliced down to a desired core width, the appropriate read/write gap being formed during the bonding process of the bars. This method is used extensively for core widths down to about three mils.
However, the production of transducer cores thinner than three mils is considerably more difficult. One known method, for example, is to lap down a thicker core to a desired width, for example from five mils to one mil. The inherent disadvantage involved here is that such cores are extremely fragile and hard to handle, e.g. during positioning of these cores in the shoe apertures, and during attachment of the back plate onto the magnetic structure or during winding of the magnetic coils onto the core pieces.
Also known are apertured magnetic transducer cores in which the aperture or slot constitutes a magnetic gap cut only part way across the magnetic material. An example of such a system is illustrated and described in the aforementioned U.S. Pat. No. 3,621,153. The referenced patent discloses a structure utilizing individual bands of magnetic material which are wound with a coil and then individually wrapped around an edge of a nonmagnetic support substrate. Magnetic gaps are sequentially cut in the individual bands by means of a laser source, the gaps having a width less than the width of the bands such that a portion of the bands bridges each longitudinal end of the gap. The gaps being cut are compared to a standard or reference and the cut is then controlled to produce heads having both uniform electrical characteristics and physical alignment.
A typical embodiment disclosed in the reference patent comprises a band of high-permeability magnetic material having a width of 0.040 inch and a gap cut therein with a width of 0.038 inch and a length of 0.002 to 0.003 inch. The band portions bridging the longitudinal ends of the gaps, in this configuration, each are 0.001 inch, the bridging band portions serving to provide mechanical strength for the core structure.
One inherent disadvantage encountered with the magnetic head taught by Wenner, supra, is that within their relative dimensions, the cores do not enable the core gaps to be substantially enlarged or reduced in width for reasons that in extending the gap width, the mechanical strength required for this type of core structure would be substantially reduced. On the other hand, in reducing the gap width, the effective magnetic intensity in the gap area would proportionally be lowered due to the continuity across the resulting, enlarged bridging portions of the band.
A further disadvantage of the core structure under discussion lies in the fact that each longitudinal end of the gap defines unavoidable radii which, however small, impair the flux intensity and, hence, the magnetic response at such ends.
A further limitation of Wenner, supra, is that in the system taught, laser cutting of the magnetic material cannot effect narrow cores with very fine core gaps having good gap definitions. It should be noted that, for example, for the recording above 4000 BPI, a narrow gap having a width of about 50.mu. inches-100.mu. inches is required. Typically, laser cuts as for example applied in Wenner, supra, are much greater than 500.mu. inches.
Moreover, given the configuration and width dimensions of both the cores and core gaps of Wenner, use of the system precludes recording of media having a high track density of, for example, 800 tpi or more. As a result, the head assembly of Wenner does not, of necessity, require close, equidistant spacings between the respective center lines of the cores.